Sulfur dioxide recovery from stack gases

ABSTRACT

AN IMPROVED PROCESS FOR UTILIZING LIMESTONE SLURRY TO SCRUB SULFUR OXIDES FROM POWER PLANT STACK GAS WHICH CONSISTS OF ADDING A WEAK ACID TO A WATER SLURRY OF LIMESTONE, BEING CIRCULATED IN A STACK GAS SCRUBBER, TO SOLUBILIZE THE LIMESTONE AND HASTEN ITS REACTION WITH SULFUR DIOXIDE; SEPARATING THE SOLID REACTION PRODUCT CONSISTING OF CALCIUM SULFIDE AND SULFATE; WASHING THE REACTION PRODUCT TO RECOVER WEAK ACID AND USING THE SEPARATED LIQUOR AND WASH LIQUID ALONG WITH FRESH LIMESTONE AS MAKEUP SLURRY TO BE FED TO THE STACK GAS SCRUBBER. THE WEAK ACID SHOULDER BE STRONGER THAN CARBONIC SO THAT IT WILL REACT WITH CALCIUM IN LIMESTONE TO SOLUBILIZE IT AND DISPLACE CARBON DIOXIDE, AND IT SHOULD BE WEAKER THAN SULFUROUS SO THAT IT WILL BE DISPLACED AND RECONSTITUTED BY SULFUROUS ACID FORMED BY DISSOLUTION OF SULFUR DIOXIDE FROM STACK GAS; BENZOIC ACID MEETS THE QUALIFICATIONS AND IS HIGHLY SATISFACTORY.

DEFENSIVE PULICATION UNITED STATES PATENT OFFICE Published at the request of the applicant or owner in accordance with the Notice of Dec. 16, 1969. 869 0.6. 687. The abstracts of Defensive Publication applications are identified by distinctly numbered series and are arranged chronologically. The heading of each abstract indicates the number of pages of specification, including claims and sheets of drawings contained in the application as originally filed. The files of these applications are available to the public for inspection and reproduction may be purchased for 30 cents a sheet.

Defensive Publication applications have not been examined as to the merits of alleged invention. The Patent Oflice makes no assertion as to the novelty of the disclosed subject matter.

PUBLISHED AUGUST 31, 1971 88!) O.Gr. 1364 CLEAN STACK 6A5 WEAK ACID MAKE-UP Ca MAKE-UPiCnCOJ. CnO CMOHI ImI TANK (D CALClUM SALT or wean ACliLCcSO AND CALCIUM MAKE-UP AS SLURRY. CALCIUM SALT OF wean ACID'PLUS CALCIUM SULFATE As SLURRY. CALCIUM SULFATE A5 soun. CALCIUM SALT 0F WEAK Aclu As SOLUTION.

REACTXONS IN SCRUBEER COMPOSlTIONS srAcK GAS (5 CONTAIMNB IF A ls ACID WITH olssoclAnoN CONSTANT BsrwEEN h co; AND H2303 USE OF WEAK ACIDS TO IMPROVE LIME SLURRY SCRUBBING CLOSED LOOP OPERATION An improved process for utilizing limestone slurry to scrub sulfur oxides from power plant stack gas which consists of adding a weak acid to a water slurry of limestone, being circulated in a stack gas scrubber, to solubilize the limestone and hasten its reaction with sulfur dioxide; separating the solid reaction product consisting of calcium sulfite and sulfate; washing the reaction product to recover weak acid and using the separated liquor and wash liquor along with fresh limestone as makeup slurry to be fed to the stack gas scrubber. The weak acid should be stronger than carbonic so that it will react with calcium in limestone to solubilize it and displace carbon dioxide, and it should be weaker than sulfurous so that it will be displaced and reconstituted by sulfurous acid formed by dissolution of sulfur dioxide from stack gas; benzoic acid meets the qualifications and is highly satisfactory. 

